Machines such as wheel loaders, excavators, dozers, motor graders, and other types of heavy equipment use multiple actuators supplied with hydraulic fluid from one or more pumps on the machine to accomplish a variety of tasks. These actuators are typically velocity controlled based on, among other things, an actuation position of an operator interface device. In particular, when an operator moves a particular interface device to a specific displaced position, the operator expects a corresponding hydraulic actuator to move at a predetermined velocity in a desired direction. During operation, however, it may be possible for the operator to request multiple actuators to move at velocities that together cause the supply pump to exceed a torque limit and/or a power output of the engine driving the pump. If left unchecked, it may be possible for the operator to request velocities that cause the engine to stall and/or operate inefficiently.
One attempt to reduce the likelihood of engine stall caused by operation of a machine's hydraulic system is disclosed in U.S. Patent Publication 2010/0154403 of Brickner et al. that published on Jan. 24, 2010 (the '403 publication). In particular, the '403 publication describes a hydraulic system having a variable displacement pump driven by an engine to supply pressurized fluid through a plurality of valves to a corresponding plurality of actuators, and a controller in communication with a manual control device and the valves. The controller is configured to receive from the manual control device desired velocities for each of the actuators, and from the engine a pump torque limit. The controller is further configured to determine flow rates for the actuators corresponding to the desired velocities, and a flow limit based on the pump torque limit. The controller is then configured to calculate a reduction ratio equal to the pump torque flow limit divided by the sum of the desired flow rates, and then apply that ratio to each of the determined flow rates before corresponding commands are directed to each of the valves. The reduced ratios help to ensure that the commanded flow rates together will not demand a pump torque greater than the torque limit required by the engine.
Although the system of the '403 publication may help to reduce the likelihood of engine stall, it may be less than optimal. In particular, the system of the '403 publication may not consider other factors affecting valve flow and pump torque such as pump flow capacity, actuator stall, flow correction, or gravity assistance.
The disclosed hydraulic control system is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.